Closures Which Contain Reservoirs and Allow Acoustic Ejection

ABSTRACT

In an aspect of this invention, a closure for a well plate is provided which has a reservoir. The closure has openings through which acoustic ejection of fluid droplets can take place without removing the closure. The reservoirs in the closure may help to maintain acceptable levels of solvent in the wells of the well plate despite the evaporation which may occur during the course of ejection.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 60/936,586, filed Jun. 20, 2007, which is incorporated by referenceherein in its entirety.

TECHNICAL FIELD

This invention relates generally to containers for fluids, and inparticular to containers for small quantities of fluid used in chemicaland biomedical research and development.

BACKGROUND

In chemical and biomedical research and development, it is common tomanipulate large numbers (e.g., thousands) of fluid containers whichmust be readily and automatably opened and closed, and yet must also bestored for months or years. The need to open and close the containersreadily tends to induce the use of relatively poorly sealed containers,whereas the desire to store the containers for months or years tends tomake it desirable to achieve tight sealing, for example to avoidevaporation loss and contamination from the outside.

The fluid containers used in chemical and biomedical research aresubject to substantial chemical compatibility constraints, for examplethat they should not be made of materials which would be attacked by thesolvents which they are designed to hold. Such constraints will alsoapply to the closures of such fluid containers. Adhesives are generallynot preferred for closure of such fluid containers because of concernsabout contamination and nonuniformity arising from adhesive residue leftover from one closure to the next.

Examples of fluid containers widely used in chemical and biomedicalresearch and development are well plates and micro tubes. Well platesare commonly used which have 96, 384, and 1536 wells, although othernumbers of wells are also in use. The dimensions and othercharacteristics of well plates have been standardized by the Society forBiomolecular Screening. A common size of well plate is 127.76 by 85.48by 14.35 mm. Well plates are commonly designed to be stacked on top ofeach other in storage. Microtubes are commonly used in racks of 96 or384. These racks of microtubes conform to dimensions similar to thelength and width of well plates so they can be handled by similarrobotic and automation equipment.

For well plates, a wide variety of lids have been developed. An exampleof a well plate lid of the prior art is described in U.S. PatentApplication Publication No. 2003/0108450. That well plate lid uses theweight of the lid to provide the force which holds the lid to the wellplate. The lid is stated to weigh 400 g preferably. A compliant sealingmember, preferably of silicone rubber, forms part of the lid and ispressed against the well plate.

There have also been efforts in the art to adapt to evaporation losses.In particular, in some cases the outer wells of a well plate are notused to hold fluids of interest but instead are filled with a volume ofthe solvent in which those fluids are stored. This solvent in the outerwells has been observed to reduce the rate at which the solvent in theinner wells evaporates. The outer wells are sometimes referred to as“moat wells” when so used.

An alternative means to adapt to evaporation losses is to periodicallyaudit the fluid levels in the reservoirs of the container and to addsolvent to those reservoirs as needed. U.S. Pat. No. 6,932,097 describesa convenient automatable way of carrying out the auditing by means offocused acoustic energy. A variety of patent applications to the presentassignee describe generally the process of acoustic ejection as employedin chemical and biomedical research, for example U.S. Pat. Nos.6,416,164 and 6,612,686.

The assignee of the present application has previously filed U.S. PatentApplication Publication No. 2006/0201948, which disclosed an approach todealing with evaporation losses which involves the use of closures whichcontain reservoirs for additional fluid. Such closures are effective inreducing the loss from evaporation.

U.S. patent application Ser. No. 11/698,004 (U.S. Patent ApplicationPublication No. 2007/0175897), also assigned to the assignee of thepresent invention, discloses a further approach to dealing withevaporation losses through closure design.

When well plates are supplied with an appropriate closure, they may bestored for considerable periods of time, at least on the order ofmonths, without a damaging loss of fluid in the wells themselves.However, the purpose of storing fluids in well plates is generally to atleast occasionally remove fluid for testing purposes. The process ofremoving fluid is often carried out by means of acoustic ejection.

The removal of fluid from a well plate generally implies removing thewell plate's closure. The closure may remain off for a considerable timeif fluid is removed from multiple wells in the well plate. It ispossible to remove quite small quantities of fluid and use them intests, for example quantities on the order of picoliters. In such acontext it is quite possible that the evaporation losses caused by theremoval of the closure to be comparable to or exceed the fluid removedfor purposes of experimentation.

There is still a need to provide well plate closures which are furthereffective in dealing with evaporation losses and in particular lossesthat occur when fluid samples are removed from a well plate.

SUMMARY OF THE INVENTION

In an aspect of this invention, a closure for a well plate is providedwhich has a reservoir. The closure has openings through which acousticejection of fluid droplets can take place without removing the closure.The reservoirs in the closure may help to maintain acceptable levels ofsolvent in the wells of the well plate despite the evaporation which mayoccur during the course of ejection.

In another aspect of this invention, a method of acoustically ejecting afluid sample comprising a solvent is provided. The fluid sample isplaced in a first reservoir. The reservoir is covered with a firstclosure. The first closure is then removed and replaced with a secondclosure. Without removing the second closure from the first reservoir, adroplet of fluid is acoustically ejected from the first reservoir.

FIGURES

FIGS. 1A-1C depict schematically closures of the invention which haveopenings which allow droplets to be ejected from a well plate while itis covered with the closure.

FIG. 2 depicts schematically a further closure of the invention whichhas multiple reservoirs for different solvents.

FIGS. 3A-3C depict schematically different views of a closure of theinvention arranged to allow easy refilling of the closure reservoirs.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Before describing the present invention in detail, it is to beunderstood that this invention is not limited to specific solvents,materials, or device structures, as such may vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include both singular and plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to “a well” includes a plurality of active ingredients as wellas a single active ingredient, reference to “a temperature” includes aplurality of temperatures as well as single temperature, and the like.

In describing and claiming the present invention, the followingterminology will be used in accordance with the definitions set outbelow.

The term “fluid” as used herein refers to matter that is nonsolid, or atleast partially gaseous and/or liquid, but not entirely gaseous. A fluidmay contain a solid that is minimally, partially, or fully solvated,dispersed, or suspended. Examples of fluids include, without limitation,aqueous liquids (including water per se and salt water) and nonaqueousliquids such as organic solvents and the like. As used herein, the term“fluid” is not synonymous with the term “ink” in that an ink mustcontain a colorant and may not be gaseous.

“Optional” or “optionally” means that the subsequently describedcircumstance may or may not occur, so that the description includesinstances where the circumstance occurs and instances where it does not.

The term “reservoir” as used herein refers to a receptacle or chamberfor containing a fluid. A reservoir may also be a volume of a memberwithin which a fluid is constrained or held.

The term “closure” as used herein refers to a member used to close acontainer for fluids. It thus encompasses for example lids, stoppers,and caps. A container may be closed with one closure or, in some cases,with multiple closures. Closures normally meet with containers atrespective surfaces on each member. The mechanical match of the closureand container at the surfaces where they meet may not be perfect, sothat some exchange of vapor between the inside and outside of thecontainer may be possible even with closures in place.

While the principles of the invention are described primarily inrelation to well plates, it should be understood that they apply equallyto other containers such as storage tubes or microtubes which maycontain fluids which are subject to acoustic ejection and for whichavoiding evaporation loss is of interest. For convenience, containerswhich are closed with the closures of the invention may be referred toas “primary members.”

In an aspect of this invention, a closure for a well plate is providedwhich has a reservoir. The closure has openings through which acousticejection of fluid droplets can take place without removing the closure.The reservoirs in the closure may help to maintain acceptable levels ofsolvent in the wells of the well plate despite the evaporation which mayoccur during the course of ejection.

Solvents used commonly in chemical and biomedical research may behygroscopic. In particular, it is well known that DMSO is quitehygroscopic and that DMSO solutions will commonly draw humidity from theambient air. In many circumstances this phenomenon whereby a fluid ofinterest comprising a hygroscopic solvent draws humidity from theambient air is undesirable. Hydration of DMSO, for example, may makecertain substances less soluble in the DMSO-water mix. A closure whichhas reservoirs of solvent can help not only to keep evaporation fromoccurring but also to keep the fluids in the individual wells fromdrawing undesirable humidity from the ambient air during the process ofacoustic ejection.

In a possible practical use of the closures of the invention, a wellplate is brought in which has a storage closure. The storage closure isremoved from the well plate, for example by means of a robot. A closureof the invention is then placed onto the well plate, and it is thenplaced inside an apparatus suitable for acoustic ejection of fluid fromthe well plate. The apparatus may be any type of acoustic ejectiondevice which is able to handle well plates of the appropriate size.Ejection then takes place through the openings in the closure.

The closure may further comprise a thin plate which covers the wellplates but contains openings through which acoustic ejection of fluiddroplets can take place. These openings in the thin plate are preferablyaligned with the ejection openings in the closure.

The openings in the closure are preferably circular. The diameter of theopenings may be determined on the basis of two factors: the size of thedroplets to be ejected from the well plate and the ease or difficulty ofaligning the openings precisely with respect to a reference known to thecontrol of the acoustic ejection apparatus. A lack of alignment mayarise for example because of imprecision in the positioning of theclosure relative to the well plate, dimensional variation in the closureor the well plate, or inaccuracy in the control's knowledge of theposition of the well plate.

Openings of diameter about 1 mm, about 1.5 mm, or about 2 mm are foundto be useful. Smaller openings may also prove beneficial and can appliedin circumstances where transducer position, droplet trajectories, andthe location of the openings in the closure are well controlled. Forexample, openings that are four times the diameter of the droplet wouldminimize gas exchange through the opening, yet still enable transfer ofthe droplet from the well through the opening. With more precisephysical alignment, an opening about two times the diameter shouldsuffice, so droplets of 150 microns in diameter could be accommodated by300 micron openings.

In general each ejection opening in the closures is preferablypositioned so that it will lie above the center of a well when theclosure is deployed on a well plate. There may be openings for all wellsof the well plate or only for some wells, where for example particularwells are used for purposes other than holding fluids which might beacoustically ejected from the well plate.

FIG. 1A schematically depicts an arrangement of closure and well plateas described above. The well 10 holds a quantity of fluid. Above thewells is a thin plate 12 with openings such as 14. Above the plate isthe main part 16 of the closure, which comprises a reservoir 18. In thereservoir 18 there may be a substance 20 which absorbs fluid, forexample felt.

It may be seen that in FIG. 1 there are at least three zones for vapor,linked by small openings. There is a first zone immediately above eachof the wells, there is a zone between the thin plate 12 and the mainpart 16 of the closure, and there is then a zone within the closurereservoir 18. The third zone may open directly into the acousticejection opening 22 as depicted in the figure. The third zone may alsoopen to the second zone through suitable apertures (not shown in thefigure).

FIGS. 1B and 1C schematically depict other closures of the invention. InFIG. 1B the opening 14 in the thin plate 12 has a smaller diameter thanthe opening 22 in the main part of the closure. For example, if thealignment of the opening 14 with the well center is more precise thanthe alignment of 22, then it may be desirable to have 14 be smaller insize than 22. In FIG. 1C there is no thin plate 12, and the opening 22in the main part of the closure is narrower at the bottom (facing thewell plate) than at the top where it opens up to the outside.

FIG. 2 schematically depicts an arrangement of closure and well plate inwhich there are multiple reservoirs 40, 42, 44 in the closurecorresponding to different solvents which are used in different wells46, 48, 50 of the well plate. In this case there is no thin plate as inFIG. 1; the closure lies directly atop the well plate. Thisconfiguration is desirable where different solvents are present in thewells since gas exchange between the closure reservoir and itscorresponding well (i.e., 40 and 46) may be greatly enhanced relative tothe gas exchange between the adjoining wells (in this example, 46 and48).

A wide variety of closure structures may be used which contain suitableopenings through which the ejected fluid may pass and reservoirs in theclosure. In general, reservoirs in the closure provide “sacrificial”fluid to maintain a high vapor pressure in the openings and in thevicinity of the closure on the side facing towards the wells. When thereis such a high vapor pressure, molecules of evaporated fluid whichescape outside from the vapor above a well will be compensated bymolecules of fluid from the reservoirs in the closure which come intothe area between wells and closure, preventing evaporation loss of fluidfrom the reservoirs. As depicted in FIGS. 1A-1C and 2, it is generallypreferred that at least one closure reservoir open into each of theejection openings in the closure, thus feeding the ejection opening withappropriate vapor.

In the invention it is preferred to be able to replenish the fluid inthe closure reservoirs periodically. In this way, these reservoirs willalways have an adequate supply of fluid, for example of solvent. Thisperiodic replenishment could take place by removing the closure from thecontainer, potentially inverting the closure or otherwise altering itsorientation, and using some sort of fluid transport system to dispensefluid into the reservoirs through openings that open into the interiorof the container. The fluid transport system could be, for example,manual pipetting, an automatic pipetting system, a tip-based transportsystem, or an acoustic ejection system. One method would be to dispensefluid directly into each opening in a manner suitable for its transportinto the corresponding closure reservoir. Another embodiment would havea deposition of fluid supply the closure reservoir around multipleopenings. For example, a lid with 384 openings could have the closurereservoir around the 384 openings supplied with fluid from a singledispense from a 96-tip pipetting system. Each tip would supply fluid toa fluid loading point in the lid that provides a transport means to thevicinity of the four surrounding openings.

FIGS. 3A-3C depict different views of a possible arrangement of inletssuch as 26 in a closure which can be used to replenish the solvent in aclosure reservoir. FIG. 3A depicts a top view, while FIG. 3B depicts asection through the line A-A in FIG. 3A, and FIG. 3B depicts a sectionthrough the line B-B in FIG. 3A. The closure depicted in FIGS. 3A-3Ccontains an absorbent material 20 which has openings which enclose theejection openings in the closure. This absorbent material 20 is placedbetween an upper portion 28 and a lower portion 30 of the closure. Inboth the upper portion 28 and lower portion 30 of the closure there areopenings for ejection, as may be seen in FIG. 3B. In the upper portion28 there are also inlets like 26 which serve for loading of fluid fromthe top of the closure, even when the closure is in place on a wellplate. This enables replenishment of the fluid in the closure reservoirswithout removing the closure from the well plate. As may be seen, thereis one inlet like 26 for each four ejection openings, so that forexample if there are 384 wells and 384 ejection openings, the fluid inthe closure reservoirs can be replenished from a 96-tip pipettingsystem.

Similarly, a 384 tip system could supply a 1536-opening lids, and othertip systems could be used to load higher density opening lids.

Similar filling schemes could be designed by one of ordinary skill inthe art to enable loading into closure reservoirs like 40, 42 and 44depicted in FIG. 2. Each closure reservoir would be expected to have atleast one loading point like 26 in FIG. 3.

Alternatively, the closure could be designed to have a removable coveror plug, or alternatively a septum plug, for example from a manufacturersuch as ABgene (Epsom, United Kingdom). The reservoirs would have one ormore openings which open into the interior of the container and anotheropening which is exposed when the removable cover or plug is removed.The replenishment of the fluid in the reservoirs of the closure could beperformed by removing the cover or plug, dispensing fluid, and thenreplacing the cover or plug. With suitable control of the dispensingprocess so as to cause a low impact of the added fluid on the mass offluid already present in the closure reservoirs, and if the openingsthat open into the interior of the container are sufficiently small, theaddition of fluid would not cause any fluid to travel from thereservoirs into the interior of the container. It would be possible, forexample, to dispense into reservoirs which do not have openings to theinside of the closure and then to allow the dispensed fluid to travelslowly through suitably sized channels from these reservoirs to otherreservoirs which have such openings. The fluid transport system usedcould again be, for example, an automatic pipetting system, or atip-based transport system, or an acoustic ejection system.

It could alternatively be practical simply to have permanent openingswithout a stopper or the like which allow the closure reservoirs to berefilled from the side facing outwards from the well plate.

In the reservoirs of the closures of the invention, it may be desirableto use a material which absorbs a desired solvent or other fluid readilyin order to concentrate that fluid where the material is placed. A widevariety of materials which absorb particular solvents well may be usedfor this purpose. Felt is an exemplary such material. Woven or non-wovenfibers, for example, cellulosic fibers, may be used. A variety of foamsmay also be employed. Foams may include, for example, open-cell foamswhich have connected voids so they have the ability to hold substantialquantities of liquid and to allow the liquid to move throughout theextent of the foam. Where the solvent is DMSO, a foam that couldwithstand long-term exposure to DMSO like a polyethylene foams would bepreferred. An open-cell polyethylene is OPCELL (described athttp://www.chimeng.com.tw/e-opcell.htm) from Chi Meng Industry (Tainan,Taiwan). The use of materials which absorb fluid may help to reduce thechance of non-gaseous transfer of material (e.g., dripping) from theclosure reservoirs to the wells.

The fluids of interest in the invention may be any fluid which is beingused in research, development, manufacturing, education or otheractivities requiring fluid handling. In particular, the fluids ofinterest may contain biological samples such as living organisms ormaterials derived from such organisms. They may form part of librariesof compounds generated through combinatorial chemistry or otherwise.They may comprise biomolecules or they may comprise synthetic ornaturally occurring organic or inorganic molecules.

The reservoirs in the closure may be of a wide variety of shapes. Theymay be simple indentations, for example of hemispherical or cylindricalshape, arranged around the contact zone on the inside of the closure. Areservoir may simply be a groove arranged around the contact zone on theinside of the closure. Alternatively, it may be a compartment ofsubstantial size spanning much of the closure.

It is preferable that closures be capable of easy opening and closing.In many cases, the closures of the invention will be adapted to beingopened and closed by means of robot arms of the type which are commonlyused for the manipulation of containers in chemical and biomedicalresearch. Thus, for example, it is preferable if the closure can be putin place by lowering it into position, and then opened simply by liftingit out of position. It is also preferred that the force of the earth'sgravity suffice to hold the close in place. It is preferred that theforce of the earth's gravity suffice to form the seal between closureand well plate.

Among the considerations which are relevant to the design of the closurethe following may be noted.

First, it may be preferred that the total volume of the container withthe closure in place be reduced to something close to the minimum volumewhich is necessary to contain the fluids of interest. The greater thehead space inside the container, the greater the amount of fluid thatmust evaporate to establish a partial pressure approaching the vaporpressure.

Second, to the extent fluid is held in the closure reservoirs throughsurface forces, it is preferred that these surface forces be sufficientto retain the fluid in its position when the closure is subject to theinevitable forces which accompany the process of closure insertion andremoval. Preferably, the process of insertion and removal does notsubject the closure to significant forces, but in practice, to theextent this process is carried out by a human or by a general purposerobot arm, there will be some degree of impact of the closure on thewell plate, resulting in a more or less sharp deceleration of theclosure. It is preferred in particular that certain free surfaces of thefluid retained in the closure reservoirs lie approximately parallel tothe direction of the impact force.

Third, while plugs and/or covers for the closure reservoirs areindicated as being desirable, it is also desirable to allow some abilityfor gases to enter and leave the closure reservoir as for example with asmall vent. This ability prevents for example the formation of vacuumsin any air space within the closure reservoir. The use of a commerciallyavailable septum plug may provide an adequate degree of venting for thispurpose.

Fourth, the reservoirs in the closures will generally contain someamount of liquid and a headspace with some amount of gas. Some of theliquid may be free and some of the liquid may be absorbed on anabsorbent material such as felt. It is in general desirable that thereservoirs in the closures, and the openings between them and thevarious zones in which vapor is present, not allow liquid to spill outof the closure reservoirs and onto the well plate. Placing too muchliquid in the closure reservoirs when they are refilled could lead tosuch spilling, as could movement of the closure when it is put on thewell plate or removed.

A figure of merit for the closures of the invention is the extent towhich they prevent evaporation of a particular solvent (e.g., water,acetonitrile) compared to not having the closure in place. It may bedesired that a closure, with its reservoirs filled to design capacitywith the solvent, diminish the evaporation rate of the solvent to nomore than about 30%, no more than about 10%, or no more than about 3% ofwhat the rate would be without the closure in place.

An alternative figure of merit for the closures of the invention is thepercentage of the solvent escaping through the ejection openings andthrough the seal between closure and well plate which comes from theclosure reservoirs. It may be desired, for example, that this percentagebe at least about 10%, at least about 25%, or at least about 50%.

Extensive guidance with respect to the formation of a good seal betweena closure and a well plate may be found in U.S. Patent ApplicationPublication No. 2006/0201948 and U.S. patent application Ser. No.11/698,004 (U.S. Patent Application Publication No. 2007/0175897).

The choice of material for the formation of the closures and containersof the invention is constrained also by the need to be compatible withthe fluids of interest. Among these, fluids where DMSO by itself or DMSOand water are solvents are of particular interest in chemical andbiomedical research. Materials which are compatible with DMSO includecyclic olefin co-polymers (COC), polyethylene (PE), polypropylene (PP),ethylene-propylene rubber (EPR) and polytetrafluoroethylene (PTFE). COCis made by Ticona Engineering Polymers (Summit, N.J.), which is part ofCelanese Corporation, and goes by the trade name Topas. One preferredTopas resin is 8007. These materials may advantageously be used to formthe closures used in the invention. In general, the closure ispreferably readily manufacturable, most preferably by injection moldingof a single component or of two or three components subsequently broughttogether.

The closures of the invention may be manipulated as part of an automatedsystem. An overall laboratory automation system may include, forexample, a carousel for holding well plates, a robot arm for moving wellplates from one instrument to another, a variety of analyticalinstruments and reaction chambers, a pin based fluid transfer system,and/or an acoustic ejection system. The overall purposes of the systemmay include taking quantities of fluids and subjecting them to analyses(including for example the ascertainment of their composition andphysical properties), reactions designed to produce particular moieties,and purification steps, all the while potentially keeping track, bycomputerized or other means, of the origin and destination of each fluidin the system and of the processes and results for each fluid. Thesystem may also be employed to generate for further use objects whichcontain or are coated with fluids moved by the system. The system mayalso track the status of each reservoir-containing closure, for examplethe last time the reservoirs in the closure were filled or thesolvent(s) or other fluid(s) in the closure's reservoirs.

The tracking of the origin, destination, processes, and results for eachfluid may be performed, for example, by having controllers such as thefluid transport system controller communicate that information to ageneral purpose computer which stores the information as flat files orin a database. Fluids are conveniently identified by assigning anidentifier to each well plate in the system and by tracking what is doneto each well in each plate at particular times in a way that allows oneto produce an overall history for the contents of each well of eachplate. It must be kept in mind in this regard that not all changes influids in the system take place as a result of deliberate or plannedaction; some may be inevitable changes that occur as a result of thepassage of time, as for example the absorption of water from thesurrounding air or the evaporation of fluids in storage, which thecontainers and methods of the present invention are concerned with.

In a laboratory automation system it will generally be necessary tointegrate equipment from different manufacturers. In this connection theadherence to particular standards may be a desirable feature of a fluidtransport system. Certain fluid transport and storage systems which formpart of a manufacturing environment may be required to meet furtherstandards relating to manufacturing as well as being able to supportoverall system conformance with the norms of “Good ManufacturingPractice” (GMP) as understood by the pharmaceutical industry.

It is to be understood that while the invention has been described inconjunction with the preferred specific embodiments thereof, that theforegoing description and the examples that follow are intended toillustrate and not limit the scope of the invention. Other aspects,advantages, and modifications within the scope of the invention will beapparent to those skilled in the art to which the invention pertains.

All patents, patent applications, and publications mentioned herein arehereby incorporated by reference in their entireties. However, where apatent, patent application, or publication containing expressdefinitions is incorporated by reference, those express definitionsshould be understood to apply to the incorporated patent, patentapplication, or publication in which they are found, and not to theremainder of the text of this application, in particular the claims ofthis application.

1. A container for fluids which can be open or closed, comprising: (a) aprimary member comprising one or more primary member reservoirs forholding a quantity of fluid, (b) a closure containing one or moreclosure reservoirs for holding a quantity of fluid, (c) wherein theclosure contacts the primary member at a contact zone, (d) wherein atleast some of the one or more closure reservoirs have an opening to theinside of the container, and (e) wherein the closure comprises one ormore apertures through which fluid may be transported with the closurein place contacting the primary member at the contact zone.
 2. Thecontainer of claim 1, wherein the quantity of fluids in the one or moreclosure reservoirs may be replenished without opening the container. 3.The container of claim 1, wherein the one or more closure reservoirs areof a size, shape, and composition such that pure water at roomtemperature and atmospheric pressure will remain in them on account ofsurface forces irrespective of the closure's orientation with respect tothe earth's gravitational field.
 4. The container of claim 1, wherein atleast some of the one or more closure reservoirs have openings to theinside of the container close to the contact zone.
 5. The container ofclaim 4, wherein all of the one or more closure reservoirs have openingsto the inside of the container close to the contact zone.
 6. Thecontainer of claim 1, wherein the primary member is a well plate.
 7. Thecontainer of claim 1, wherein the primary member is a microtube or rackcontaining a plurality of microtubes.
 8. The container of claim 1,wherein the primary member and the closure are made of materials whichare compatible with DMSO.
 9. The container of claim 1, wherein, when thecontainer is so oriented in a closed position that the closure liesabove the primary member in a substantially horizontal orientation, theforce of the earth's gravity suffices to hold the closure in place. 10.The container of claim 9, wherein, when the container is so oriented ina closed position that the closure lies above the primary member in asubstantially horizontal orientation, the force of the earth's gravitysuffices to create a seal between closure and primary member.
 11. Thecontainer of claim 1, wherein the closure comprises a reservoir forhumectant which has an opening to the outside of the container when thecontainer is closed.
 12. The container of claim 11, wherein a solventcomponent of at least one fluid in the primary member is absorbed by thehumectant in the closure reservoir.
 13. The container of claim 1,wherein one of the materials present at the contact zone is a compliantmaterial.
 14. The container of claim 13, wherein the compliance of thematerial present at the contact zone increases in the presence of afluid.
 15. The container of claim 14, wherein the fluid in whosepresence the compliance increases is water or DMSO.
 16. The container ofclaim 1, wherein the closure comprises a volume of a material which canhold 10 times its dry weight in DMSO.
 17. The container of claim 16,wherein the closure comprises a volume of a material which can hold 20times its dry weight in DMSO.
 18. The container of claim 1, furthercomprising structures on the outside of the container which retarddiffusion of gas from the vicinity of the contact zone to thesurrounding ambient.
 19. The container of claim 1, wherein the one ormore apertures have a diameter of no more than about 1 mm.
 20. Thecontainer of claim 1, wherein at least one reservoir in the closureopens to one or more apertures.
 21. The container of claim 6, whereinthe closure comprises one reservoir which opens to particular wells ofthe well plate and another reservoir which opens to a disjoint set ofwells of the well plate.
 22. The container of claim 6, furthercomprising a thin plate with openings for acoustic ejection placedadjacent to the well plate.
 23. A method of storing a plurality of fluidsamples all comprising a solvent, the method comprising the steps of:(a) storing each fluid sample of the plurality in a well of a wellplate, (b) covering the well plate with a closure which comprises areservoir holding a quantity of the solvent, and (c) acousticallyejecting a portion of the contents of a well while the well plateremains covered with the closure.
 24. The method of claim 23, where thereservoir in the closure has an opening allowing exchange of gas with atleast some of the wells of the well plate.
 25. The method of claim 23,where at least 10% of the solvent escaping to the atmosphere through theseal between the closure and the well plate and through the ejectionopenings comes from the solvent in the closure.
 26. A method ofacoustically ejecting a fluid sample comprising a solvent, the methodcomprising the steps of: (a) placing the fluid sample in a firstreservoir, (b) covering the first reservoir with a first closure, (c)removing the first closure, (d) covering the first reservoir with asecond closure comprising a second reservoir containing a quantity ofthe solvent, and (e) without removing the second closure from the firstreservoir, acoustically ejecting a droplet of fluid from the firstreservoir.
 27. The method of claim 26, where the second reservoir has anopening allowing exchange of gas with the first reservoir.
 28. Themethod of claim 26, where at least 10% of the solvent escaping to theatmosphere through the seal between the second closure and firstreservoir comes from the solvent in the second closure.
 29. The methodof claim 26, wherein the first closure comprises a reservoir containinga quantity of the solvent.
 30. A closure for a container comprising (a)at least one opening through which a droplet of fluid may beacoustically ejected, (b) at least one reservoir for fluid which opensto at least one opening, and (c) a contact zone for contacting thecontainer, wherein the container has evaporation rate of water in thecontainer with the closure in place and the at least one reservoir inthe closure filled is no more than about 10% of the evaporation rate ofthe same volume of water in the container without the closure in place.31. The closure of claim 30, wherein the closure is suitable for usewith a well plate.
 32. The closure of claim 31, wherein the closure hasat least one opening through which a droplet of fluid may beacoustically ejected corresponding to each of a majority of the wells inthe well plate.